// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Collections.Generic;
using System.Threading.RateLimiting;

namespace FlyingEye.Middlewares.RateLimiting
{
    internal sealed class DefaultCombinedLease : RateLimitLease
    {
        private readonly RateLimitLease _globalLease;
        private readonly RateLimitLease _endpointLease;
        private HashSet<string>? _metadataNames;

        public DefaultCombinedLease(RateLimitLease globalLease, RateLimitLease endpointLease)
        {
            _globalLease = globalLease;
            _endpointLease = endpointLease;
        }

        public override bool IsAcquired => true;

        public override IEnumerable<string> MetadataNames
        {
            get
            {
                if (_metadataNames is null)
                {
                    _metadataNames = new HashSet<string>();
                    foreach (var metadataName in _globalLease.MetadataNames)
                    {
                        _metadataNames.Add(metadataName);
                    }
                    foreach (var metadataName in _endpointLease.MetadataNames)
                    {
                        _metadataNames.Add(metadataName);
                    }
                }
                return _metadataNames;
            }
        }

        public override bool TryGetMetadata(string metadataName, out object? metadata)
        {
            // Use the first metadata item of a given name, ignore duplicates, we can't reliably merge arbitrary metadata
            // Creating an object[] if there are multiple of the same metadataName could work, but makes consumption of metadata messy
            // and makes MetadataName.Create<T>(...) uses no longer work
            if (_endpointLease.TryGetMetadata(metadataName, out metadata))
            {
                return true;
            }
            if (_globalLease.TryGetMetadata(metadataName, out metadata))
            {
                return true;
            }

            metadata = null;
            return false;
        }

        protected override void Dispose(bool disposing)
        {
            List<Exception>? exceptions = null;

            // Dispose endpoint lease first, then global lease (reverse order of when they were acquired)
            // Avoids issues where dispose might unblock a queued acquire and then the acquire fails when acquiring the next limiter.
            // When disposing in reverse order there wont be any issues of unblocking an acquire that affects acquires on limiters in the chain after it
            try
            {
                _endpointLease.Dispose();
            }
            catch (Exception ex)
            {
                exceptions ??= new List<Exception>();
                exceptions.Add(ex);
            }

            try
            {
                _globalLease.Dispose();
            }
            catch (Exception ex)
            {
                exceptions ??= new List<Exception>(1);
                exceptions.Add(ex);
            }

            if (exceptions is not null)
            {
                if (exceptions.Count == 1)
                {
                    throw exceptions[0];
                }
                else
                {
                    throw new AggregateException(exceptions);
                }
            }
        }
    }
}